Many synthetic resins which may be formed by emulsion polymerization are well known in the art. It is not difficult to form stable aqueous dispersions of such resins by addition of the resin feed, an appropriate dispersing agent and catalyst to water with stirring. However, emulsification of resins produced by other polymerization techniques requires that the bulk polymer must be dispersed in water to obtain an aqueous dispersion. Such a type is the hydrocarbon resins produced from steam-cracked petroleum fractions.
These hydrocarbon resins, i.e. petroleum resins, are defined herein at the thermoplastic resins obtained by polymerization, in the presence of a catalyst of the Friedel-Crafts type, of steam cracked petroleum distillates, boiling in the range between about 30.degree. C. and 280.degree. C., or any fraction of these distillates boiling within the said range, or of mixtures of olefins and diolefins containing sufficient diolefins to obtain a resin and not an oil. This polymerization is performed at tempertures which range generally from 0.degree. to 70.degree. C., and preferably from 30.degree. C. to 55.degree. C.
These resins are polydienic in character and can have a ring and ball softening point between about 38.degree. C. and 180.degree. C.
Since these resins are solid at room temperature numerous approaches have been utilized to produce aqueous emulsions of said resins for application as an adhesive, as a saturant or coating for paper or cloth or as a sizing or binding material in paper pulp.
One approach was to solvate the resin in hydrocarbon solvent and then combine resin solution and water. Invariably some residual hydrocarbon solvent remains in the finished emulsion, and this is undesirable in certain applications. This has led to the development of solvent-free dispersions (see U.S. Pat. No. 2,809,948) and emulsions (see U.S. Pat. No. 3,377,298) of petroleum resins. In both of these formulations, ionic emulsifiers have been utilized; in the former a mixture of cationic and non-ionic surface active agents is used to achieve a resin dispersion; and, in the latter an ionic surfactant is used in combination with an aqueous gel of a swelling earth to produce an emulsion paste of a petroleum resin.
Petroleum resin emulsions containing substantial amounts of plasticizers or diluents such as linseed oil and waxes and paraffins are taught in French Pat. No. 1,452,875 and German Offen. No. 2014652 respectively. However, such large percentages of diluent can materially modify, not always favorably, the properties of the base resin.
Emulsion pressure sensitive adhesives desirably should be comprised of aqueous emulsions of tackifying resins, i.e. that resin which enhances the adhesive properties of an emulsion polymer system used as an adhesive. It is highly desirable that raw materials added to the tackifier resin emulsion for primarily other than tack or adhesion enhancement, e.g. plasticizers or other diluents, emulsifiers, stabilizers, etc., be kept to an absolute minimum. Such materials often have an adverse effect on the functional properties, e.g. tack, adhesive properties, of the resin being emulsified.
For a general discussion of resin emulsions for emulsion pressure sensitive adhesive use (including its commercial aspects) see the published talk entitled Resin Dispersions for Water Based Pressure Sensitive Adhesives by Robert W. Wherry and presented at The Pressure Sensitive Tape Council Seminar on Water Based PSA Systems in June of 1979.
This invention has for one of its objects the preparation of highly functional, relatively high softening point, non-polar petroleum resin emulsions without the use of volatile solvents and employing minimal plasticizers, diluents or other products constructive in emulsification but potentially deleterious to the emulsion end-use.
A further object is to provide an emulsion preparation method of an inversion type for the aforementioned resins which effectively produces emulsions of small particle size and exceptional stability.
A further object is provision of aqueous dispersions of hydrocarbon resins of high shelf and mechanical stability.
A further object is to provide petroleum resins in the form of a latex-like dispersion for application as a pressure sensitive adhesive, as a saturant or coating for paper or cloth, or as a sizing or binding material in paper pulp.